Tandem axle spring suspension



Sept. 11, 1951 A. F. HICKMAN TANDEM AXLE SPRI NG SUSPENSION 5 Sheets-Sheet 1 Filed Nov. 2, '1949 Sept. 11, 1951 A..F. HICKMAN TANDEM AXLE SPRING SUSPENSION 5 Sheets-Sheet 2 Filed Nov. 2, 1949' INVENTOR wai /MM 5r y M /zfiofizgs.

Sept. 11, 11951 A. F. HICKMAN 2,567,431

TANDEM AXLE SPRING SUSPENSION Filed Nov. 2, 1949 5 Sheets-Sheet 5 VENTOR r,

Sept N, 1951 A. F. HICKMAN TANDEM AXLE SPRING SUSPENSION 5 Sheets-Sheet 4 Filed NOV. 2, 1949 JNVENTOR flffo? 71 .9

Sept. 11, 1951 A. F. HICKMAN TANDEM AXLE SPRING SUSPENSION 5 sheets-sheet 5 INVENTOR. 4 wan/m Filed Nov. 2; 1949 Patented Sept. 11, 1951 TANDEM AX-L'E SPRING SUSPENSION Albert F. Hickman, Eden, N. Y., assignor to Hickman Industries, Inc., Eden, N. Y., a corporation of New York Application November 2, 1949, Serial N0.'1'24,96-1

8 Claims. i

This invention relates to a tandem axle spring suspension particularly for trucks in which each axle is permitted to move against :a geometric resilient resistance both laterally and longitudinally relative to the vehicle frame particularly Where the vehicle has a high percentage .of load variation. 7

The invention is particularly directed to the form of torsion rod tandem axle forming the subject of my "Patent No. 2,333,650, dated November '7, 1943, and whileit is more particularly described in connection with a truck, it is also applicable to other land vehicles such as railroad cars.

In common with the said patent important objects of the present invention are to provide a spring suspension (1) which will function to safely support the vehicle body at high "speeds, both when loaded and unloaded; (2 which reduces and cushions both the vertical and lateral impacts from the axle against the body of the vehicle, both when the vehicle is loaded and unloaded and without imposing undue end thrusts on the pivotal connections which connect the axles to the body; (3) in which torsion rods are employed to provide a longer and'variable spring resistance range; (4) in which geometric resilient resistance is obtained in a compact structure which requires no lubrication and is free from the squeaks incident to the use of leaf springs; (5) in which the distribution of the load to the body is at a plurality of spaced points; (6) in which side sway is reduced "to any desired amount; (57) in periodic vibration of the suspension is damped out and in which wheel tramp is avoided; (8) in which all forces are cushioned so .as to increase gasoline mileage and tire wear; (9) which has light unsprung weight, (10) in which the metal vstresses are within safe working limits of heat treated castings or forgings; (11) which can be produced at low cost and in particular requires only simple machining operations; (12) ,inwhichthe parts are arranged inside the wheels and in which the parts are arranged close to the wheels to provide high and wide pivot positions-andincreased stability; (13) which can easily be taken down and repaired; (14) in which any desired frequency or degree of spring deflection can be obtained; (15-) in which auxiliary devices for the control of side sway are rendered unnecessary; (16) in Which-one or both of the tandem axles-are self-steering so that when rounding a curve, said tandem axles are caused. .to assume such an :angle relative to each other as will enable a pure rolling action to be obtained; (17) whichincludes compensating means connecting the companion ends of the tandem axles and through which the excess .load on either axle is transmitted to the other axle;

(18) in which said compensating means is in the one axle to the other; (19) in which the transfer of the load from the tandem aides to the front axle of the vehicle, under braking reaction, is-

identical with the similar transfer of theload in a two-axle vehicle of the same wheelbasaweight and load; (20) in which all connections to the frame are in closely spacedrelation to each other thereby to reduce to a minimum any distortion of the suspension through weaving of the frame; ('21) in which all connections to the frame are made to the longitudinal side bars thereoi'toasim-- pli'fy application of the suspension and design :of the frame and suspension and to further reduce the effect of wearing .of the frame upon the suspension; and 1622') which wills-tand up under .conditions of severe and constant use with very little servicing.

The principal specific object of the present invention is :to provide such :a tandem :axlelspring suspension which is particularlylapplicable to all types of trucks. i

Iii-particular aspecific object is'to 'pr'ovidesuch a tandem axle torsion spring suspension to fit a truck havin .a wide .frame, and having large tires, it having been found :difiicult, with the suspension shown in the said patent to accommodate frames over thirty "inches wide with "11 inch tires. Frames 34 inches wide with '11 inch tires must be arranged for and :still have room 'for drive shaft. 7

Another specific object is to provide such a tandem axle torsion rod :spring suspension which does not require the irameto be :cut away at any high-1y stressed point to accommodate the sus. pension.

Another specific obj ect is to provide such a tandem axle torsion rod spring suspension in which the truck frame [can be arranged at a low elevation so that it can bottom on the axles. To accomplish this object it was necessary to arrange the torsion rods so that they "were not. interposed between the frame and the axles as in .my said Patent No. 2,333,650.

Another specific object is to provide such a tandem .ax-le torsion rod spring suspension having torsion rods of suificient length to'prov-ide a proper ride and-at the same timeto provide axle nompensation of :at least 18 to 12 inches without cutting away a large section of the frame at a highly stressed point to accommodate the gear box necessary to such axle compensation.

Other specific objects and advantages will appear from the following description and accompanying drawings in which:

Fig. 1 is a fragmentary top plan view, partly in section, of a truck frame supported by a tandem axle spring suspension embodying my invention.

Fig. 2 is a vertical longitudinal section thereof, taken on line 22, Fig. 1.

Figs. 3 and 4 are fragmentary vertical transverse sectional views taken on the correspondingly numbered lines of Fig. 1.

Fig. 5 is an enlarged fragmentary generally vertical section taken on line 55, Fig. 1.

Fig. 6 is a fragmentary end elevational view, viewed from the left hand of Fi 5.

Fig. 7 is a fragmentary end elevational view, viewed from the right hand of Fig. 5.

Fig. 8 is a fragmentary horizontal section taken on line 3-8, Fig. 2.

Fig. 9 is an enlarged fragmentary view similar to Fig. 8 and showing one of the frame bearings.

Fig. 10 is an enlarged fragmentary vertical section taken on line Ill-l0, Fig. 1.

Fig. 11 is a vertical section taken on line I I, Fig. 10.

Fig. 12 is an enlarged horizontal section taken generally on line |2--|,2, Fig. 2.

Fig. 13 is an enlarged generally vertical section taken on line l3-|3, Fig. 1.

This invention is shown in connection with a highway truck, the frame of which is shown as including a pair of main longitudinal side frame bars 2| of channel shape in cross section and arranged with their channels opposing each other. These side frame bars 2| of the frame are joined at their rear extremities by a cross frame bar 22 which is also shown as being channel shaped in cross section with its channel facing forwardly. For strength, diagonal brace channels 23 are preferably interposed between each side frame bar 2| and the central part of the rear cross frame bar 22 in any suitable manner. In addition the truck frame20 is shown as includin a pair of cross frame bars 24 arranged on opposite sides of the forward tandem axle and each of channel shape incross section with its channel facing downwardly. Each end of each of these cross frame bars 24 is shown as secured to the web of the corresponding main longitudinal side frame bar 2| by a pair of L-shaped brackets 25 and between these cross frame bars 24 each main longitudinal side frame bar 2| is preferably reinforced by a top plate 26 welded along one side of the underside of the top flange of the main longitudinal side frame bar 2| and extending along the upper faces of the pair of cross frame bars 24 and Welded thereto; these top plates 26 providing in effect an extension of the top flanges of the main longitudinal side frame bar 2| between the cross frame bars 24.

This frame is shown as supported by a pair of tandem axles 30 and 3| which are supported by wheels 32, these wheels being rotatably secured to the axles. One or both groups can be drive wheels, both axles being shown as provided for this purpose with differential housings 33, 34 through which power is transmitted to the drive axle shafts 35 housed within the axles 30, 3| and which are secured to the wheels 32 in the usual and well known manner.

The construction of the tandem axle spring suspension at the left hand side of the truck is the same as the tandem axle spring suspension at the right hand side of the truck and hence a description of the spring suspension at one side of the truck will be deemed to apply to both sides, the same reference numerals being used.

Referring more particularly to the front tandem axle 30, to each end of this axle is secured an axle bracket 36 which is fast to the axle and extends upwardly therefrom and is formed to provide a pair of arms or horns 31 which are spaced from each other lengthwise of the truck frame. Any suitable means can be provided for so securing each axle bracket 36 to the corresponding end of the front tandem axle 30, each axle bracket 36 being shown as having for this purpose a flat base 38 connected by four vertical bolts 39 to a bottom plate 40 arranged under the axle end. Filler blocks 4| and 42 are shown as interposed between the axle end and the flat base 38 and bottom plate 40, respectively, and can be welded to the axle end.

At their upper extremities the arms or horns 31 of each axle bracket 36 carry an axle pivot pin 43 which can be fastened to these arms or horns in any suitable manner, the details of the preferred connection between each axle pivot pin 43 and the horns or arms 31 of the corresponding axle bracket 36 being illustrated in detail in Figs. 5, 6 and 7.

As best shown in Fig. 5, the central part of this axle pivot pin 43 is enlarged as compared with its reduced ends and thi enlarged cylindrical central part of each axle pivot pin 43 is provided m'th a large relatively deep helical groove 44 having a relatively long lead, this helical groove extending from one end of the cylindrical enlarged part of each axle pivot 43 to the opposite end thereof. This long lead helical groove 44 is responsible, as discussed later, for the self-steering character of the front tandem axle as achieved by the angular inclination of the pivot pins in the said Hickman patent, and for this purpose the axle pivot pins 43 at opposite sides of the truck are identical except that the helical grooves 44 are pitched in reverse relation to each other. Each axle pivot pin 43 can additionally be provided with a helical oil groove 45.

The connection between the rear end of each .axle pivot pin 43 and the corresponding rear arm or horn 31 of the front axle bracket 36 is provided by a threaded bore 46 into which the long lead helical groove 44 of the axle pivot pin 43 screws and by a reduced hexagonal rear end 48 of the axle pivot pin 43 projecting rearwardly from the corresponding axle bracket arm or horn 31 and provided with an annular groove 49 for a snap ring 50. A washer like part 5| having a hexagonal hole fitting the hexagonal rear end 48 of the axle pivot pin 43 is interposed between the snap ring 50 and the adjacent flat vertical rear face provided at the upper end of the arm or horn 31. The lower edge 52 of this washer like part 5| is straight, as best shown in Fig. 7, and this straight edge seats upon a square shoulder 53 provided on the upper end of the rear arm or horn 31. It will therefore be seen that each washer like part 5| tends to hold the rear end of the axle pivot pin 43 against turning.

The connection between the front end of each axle pivot pin 43 and the corresponding front arm or horn 31 of the axle bracket 36 comprises a bore 54 provided in this arm or horn 31 and receiving a cylindrical reduced end 55 provided at the corresponding end of the pin 43. Beyond the reduced end 55 the pin 13 is formed to provide a hex 5.6 or other out of round cross sectional shape, and between hex 56 and the reduced part =55 the pin 43 is formed to provide a groove 58 receivingka .snapring 59. The hex 56 fits :ina hexagonal opening provided in a washer-like part 6.0, one :side .61 of which is straight or square to :fit a square shoulder 162 provided on the adjacent ann or horn 31. It will be seen that this washer-like 6!] ,is prevented from turning relative to its axle bracket arm 31 and since :it is provided with a hexagonal opening fitting the hex $6 provided on the front end of the :pin 43, the pin '43 is likewise prevented from turning relative to the *axle bracket arm 31. To retain the pin 43 against endwise displacement, its iurther reduced end 53 is threaded to receive a 'nut M, a washer 6.5 being "interposed between this nut and the washer-like part 611. Since the hex 55 is smaller than the bores :and 46, it will be seen that the pin 43 can readily be removed :by removing its nut 64 and withdrawing the pin 43 axially :to the right as viewed in Fig.

'Each axle pivot pin 43 is journalled :in =abearing bushing 66 in the upper end of a shackle 88. This bearing bushing 66 is preferably made of a lubricant impregnated material and this hearing bushing 66 is provided with a thread 69 to fit the long lead groove I provided in the axle pivot pin 43. Each shackle t8 can be of any suitable construction and is formed to provide a pair of depending arms or knuckles H1 in which opposite ends of a crank arm pivot pin ii are journalled in any suitable manner, each crank arm pivot pin 71 being arranged parallel with its companion axle pivot pin 43. As best shown in Fig. 5 it is preferred to thread the opposite ends T2 of each crank arm pivot pin 71 and to fit each of these threaded ends into a threaded bearing bushing 18 provided in the corresponding arm or knuckle T of the shackle. Each bushing 13 is preferably madeof -a lubricant impregnated material and it will be seen that such bushings permit oscillation of the shackle (i8 and at the same time prevent substantial endwise movement of the shackle relative to the crank arm pivot pin so as to resist end thrust caused by "brake and drive torque reactions against the shackles 68.

Each crank arm pivot pin "H is fast to the outer or free end of a crank arm 14 which outer or free end "is disposed between the arms or knuckles "T0 of the corresponding shackle 68. Each crank arm 14 extends "through an opening it in the vertical web of the adjacent longitudinal side frame bar 2| and its opposite 'or inner end embraces and is secured to; as by welding, a tube 16 as best shown in Figsqaa-nd *8.

This tube 1-6 is arranged within the channel of its longitudinal side frame bar 21 and extends along this longitudinal side 'frame bar 21 parallel with the axle pivot pin 4'3 and crank arm pivot pin H. On opposite sides of the crank arm M, the tube 16 is journalled in a pair of bearings indicated generally at 18 and which are identical in construction.

Each of these hearings can be of any suitable construction to permit oscillation of the tube is and at the same time resist end thrust thereof and for this purpose these hearings are shown as being of the threaded bus-hing type, illustrated in larger section in Fig. 9. -As there shown, each bearing 18 comprises an externally threaded metal sleeve 1-9 fitting around and welded to the dube i5 and the threads of which lit :in internally threaded bushing '18 preferably made of a lubricant impregnated bearing material. This threaded bushing is held in a metal holder or case 84 having a .flat base 32 which :can 'be secured in any suitable manner to the inner :face of the web of the corresponding longitudinal side irame bar 21. It will be seen that the externally threaded sleeve '19- is *free to turn in the internally threaded lubricant impregnated bushing and is held against endwise displacement by the threads. The oscillation of threaded sleeve 1'9 in the threaded bushing 33]] results, of course, in a slight endwise movement the threaded sleeve 19 and tube P6, butthis slight movement is of no consequence in the suspension.

Each tube '15 extends forwardly a substantial distance "from its *I'ront bearing H3 and at its extreme forward end has welded thereto a socket member '84 as best shown in Fig. 8. This socket member is'preferably reinforced by a surrounding ringx85 and is provided with a bore 86 the end of which can be closed by a plug 88. This bore 86 is preferably oval in cross section to receive the enlarged ovalled live end 589 of a torsion rod 90. The oval bore 86 and ovalled 'l-ive end 89 are preferably formed in the manner set forth in :my Patent'No. 2,213.;0'04, granted August '27,, 1940, for Torsion Rod Mounting.

Referring now to the rear tandem axle '31 the spring Suspension from each end of this axle to its crankarm is identical with the corresponding parts of the front tandem axle suspension and the same reference numerals have'there'fore been applied and d'istlnguished'by the .sulfix a. Thus to each end of this rear axle is secured an axle bracke't'iifia which is fast to the axle and extends upwardly therefrom and is formed to provide a pair of arms or horns 3111 which are spaced from each other lengthwise of the truck frame. Any suitable means can be provided for so securing each axle bracket 36a to the corresponding end of tandem axle 3 I, .eachaxle bracket being shown as having for this purpose a fiat base 38a connected by 'four vertical bolts 39a to a bottom plate a arranged under each axle end. Filler blocks 41a. and 42a are shown as interposed between the axle end and the fiat base 38a and bottom plate 10a, respectively, and can be welded to the .axle end.

At their upper extremities, the arms or horns 31a of each axle bracket 36a carries an .axle pivot pin 43a which can be fastened to these arms or burns in any suitable manner, the details of the preferred connection between each axle pivot pin 43a and the horns or arms 31a of the corresponding axlebracket flliabemgillustrated in detail in Fig. 13.,

.As best shown in this figure the central part of this axle pivot pin i311 is enlarged as compared with its reduced ends and this enlarged cylindrical central part of each axle pivot pin 4301s provided with a large relatively deep'helical groove 14a having a relatively long lead, this helical groove extending from one end of the cylindrical enlarged central part. of each axle pivot pin 33a to the opposite end thereof. This long lead helical groove Mn is responsible, as discussed later, for the self-steering character of the rear tandem axle as achieved by the angular inclination of the pivot pins in my. Patent No. 2,333,650 and for this purpose the axle pivot pins 43a at opposite sides of the truck are identical except that the -helical grooves 14a are pitchedin reverse relationtocadh other.

The connection between the rear end of each axle pivot pin 43a and the corresponding rear arm or horn 31a of the axle bracket 36a.is pro vided by a threaded b'or'e 46a into which the long lead helical groove 44a of the axle pivot pin 43a screws and by a reduced hexagonal rear end 48a of the axle pivot pin 43aprojecting rearwardly from the corresponding axle'bracket arm or horn 31a and provided with an annular groove 49a for a snap ring 50a. A washer-like. part Ia having a hexagonalhole fitting the hexagonal rear end 48a of the axle pivotpin 43a. isinterposed between the snap ring-50a and the adjacent flat vertical rear face provided at the upper end of the arm or horn 31a; Thelower edge- 52a;of this washer 5Ia is'straight in the same manner as with the corresponding washer 5I for the front axle pivot pin 43 and this'straight edge seats upon a square shoulder: 53a provided on the upper endof the rearaxle bracket arm 31a. It will be seen that the resting of the straight edge 52a ofthe washer member 5 Upon the shoulder 53a and the hexagonal hole in this washer member fitting the hexagonal end 48a of. the axle pivot pin 43a holds this end of this axlepivot pinagainst turning relative to this axle bracket arm.

As with the front axle bracket 36, the connection between the front end of each axle pivot pin 43a and the corresponding front arm or horn 31a of the axle bracket 36a comprises a bore'54a provided in this arm or horn 31a and receiving a cylindrical reduced end 55a provided at the corresponding end of the pin 43a. Beyond the reduced end 55a the pin 43a is formed to provide a hex, 58a or other out of round cross sectional shape, and between this hex 56a and the reduced part 55a the ,pin 43a, is formed to provide a groove 58a receiving a snap ring 59a. 4 The hex 55a fits in a hexagonal opening provided in a washer-like part,60a, one side BIa. of which is straight or squared to fit a square shoulder 52a provided on the adjacent arm or born 31a, in the same manner as with the corresponding washerlike part 60 of each front axle pivot pin43. It will be seen that this washer-like part 60a, is prevented from turning relative to its axle bracket arm 3'Ia.and since it is provided with a hexagonal opening fitting the hex 56a provided on the front end of the pin 43a, the pin 43a is likewise prevented from turning relative to the axle bracket arm 31a. To retain the pin 43a. against endwise displacement, its further reduced end 63a is threaded to receive a nut 640., a washer65a being interposed between this nut and the washer like part 60a. Since the hex 58ais smaller than the bores 54a and 46a, it will be seen that the pin 43a. can readily be removed by removing its nut 64a and withdrawing the pin 43a axially to the right as viewed in Fig. 13. v

:,As with the front axle assembly, each axle pivot pin 43a is journalled in-a bearing bushing 65a, in the upper endof a shackle 58a. This bearing bushing-55a is preferably made of, a lubricant impregnated material and thisbearing bushing 66a. is provided with-a thread 69a to fit the long leadgroove 440. provided in the axle pivot pin 43a. Each shackle 68a. can be of any suitable construction andis formed to provide a pair of depending arms or knuckles a in which oppositeends of a crank arm pivot pin 1Ia are journalled in any suitable manner, each crank arm pivot pin Ila being arranged parallel with its companion axle pivot pin 43a. As best shown in Fig. 13, it is preferred to thread the opposite ends 12a, of each crank arm pivot pin IIa,,and to fit each of these threaded endsinto a threaded bushing 13a provided in the corresponding arm or knuckle 10a of the shackle; Each bushing 13a is preferably made of a lubricant impregnated material and it will be seen that such bushings permit oscillation of the shackle 68a and at the same time prevent substantial endwise movement of the shackle relative to the crank arm pivot pin so as to resist end thrust caused by brake and drive torque reactions against the shackles Each crank arm pivot pin Ila is fast to the outer or free end of a crank arm 94 which outer or free end is disposed between the arms or knuckles 10a of the corresponding shackle 68a.

secured thereto in any suitable manner.

Each. crank arm 94 is disposed below the adjacent longitudinal side frame bar 2I as best shown in Fig. 4, and is bifurcated to form a pair of fulcrum arms 95 and 96. The forward fulcrum arm 95 of each crank arm is formed to provide a forward crank arm pivot pin 98 and which is journalled in a bearing 99. This bearing 99 can be of any suitable construction and is secured to the adjacent longitudinal side frame bar 2 I, each of the bearings 99being shown as provided for this purpose with an upwardly extending plate I00 which can be welded or otherwise secured to the outer face of this longitudinal side frame bar 2|.

The rear fulcrum arm 96 of each crank arm 94 is formed to provide a cylindrical hub or extension IOI fitted, as best shown in Figs. 10 and 11, in a bore at the rear end of the hub I02 of a gear I03 journalled in a gear box I04. This hub or cylindrical extension IOI of each crank arm 96 is also provided with an oval end socket I05 in which is fitted the ovalled end I06 of a splined member I08, the opposite end of which is enlargedand provided with splined grooves I09 fitted in the opposite end IIO of the hub of the gear I03, this end IIO of the hub of the gear I03 being splined so that the gear I03 is compelled to turn with the splined member I08, this splined member in turn being compelled to turn with the corresponding crank arm 94.

The gear case I04 is split to provide an inner section W411 and an outer section I041), these two sections being connected by screws III and each longitudinal side frame bar 2| being cut away, as indicated at II2, to accommodate the upper part of the outer section I04b of the gear box, as best shown in Fig. 2. This outer section I04b of the gear box can be secured to the adjacent longitudinal side frame bar 2| in any suitablemanner as by the provision of a flange II3 thereon which fits inside the longitudinal side frame bar 2| around the opening I I2 and can be It will particularly be noted that the longitudinal side frame bars 2I are cut at their extreme rear ends to provide the openings II2 for accommodating the gear box I94, these longitudinal side frame bars ZI, not being highly stressed at this point.

The hub ends of the gear I03 are journalled in bearings I I4 arranged in bores jointly provided by the two sections of the-gear box I04, these bearings preferably being of a lubricant impregnated material.v Each of these bearings I I4 is also preferably protected by a dust seal in the form of a rubber ringI I5 at. the outer end thereof. To permit of ready dismantling of the suspension the two sections of the gear box I04 are formed to provide an opening I I6 in line with the splined member I08 and of a sufficiently large size to permit the splined member I08 to be directly drawn rearwardly through this opening. To prevent accidental displacement of the splined member: #08, this opening H6 isprovided: with a flanged plug I I8 which can be secured to the gear case I04 by screws I I9 or in any other suitable manner.

The teeth. of the gear I03 mesh with the teeth of a gear I20, this last gear being provided with extended hubs journalled in bearings I21 carried between the two sections I04-a, IMIJ of the gear case I04 in the same manner as with the bearings I Id of the gear I03. These bearings I2I are. also preferably made of a lubricant impregnated material and are preferably protected by dust seals inthe form of rubber rings I22 at the outer ends of these hearings.

Each gear I20 is formed to provide a through bore I23 which is oval in. cross. section, this oval bore I23" receiving anenlargedoval led. rear end I24 of the torsion rod 90. As with the opposite end 89 of this. torsion rod 90, the oval bore. I23

and ovalled end I24 of the torsion rod-i are preferably formed inv the manner set forth in my Patent2,213,004, granted August 27', 1940, for Torsion Rod. Mounting.

In. the operation of the suspension the upward movement; of one end of, say, the front axle 30, through its shackle- 68', swings the outer end of its crankv arm M upwardly. This rotates the tube 16, to which this crank arm is fixed, in its bearings I8 on the adiacent longitudinal side frame bar 21.. Since the forward enlarged ovalled extremity 89' of the torsion. rod 90- is connected through. the oval bore socket member 84 Withthis torsion tube this rotation of the torsion tube imparts a twisting or torsional movement tothis live end 89 of the: torsion rod 90.

.This torque of the torsion rod 90 is transmitted through its ovalled end I24. and ova-lied bore I23 to the upper gear I20. This gear I is thereby rotated and rotates its companion gear H33- in the gearbox I04. The rotation of the gear I03 rotates the member I08 splined therein and through the ovalled end I06 of this splined member mil-rotates the rear crank arm 94. about its fulcrum pivots 98 and IN.

Because of the gears I03 and I20, this twisting of the torsion rod 90 tends to force the rear crank. arm 94 downwardly. This downward. force imposed upon the crank arm 94 for the rear axle is transmitted through its shackle. 68a directly to the corresponding end of the rear axle 3I.

It will therefore be seen that the torsion rod 90 connected through the tube 16, crank arm 14 and shackle 68 to the corresponding end of the front axle 30 and also connected through the gears I20 and I03 to-the crank arm 94 and. shackle 68a for the rear axle 3-l, provides axle compensation, thatv is; the transfer of the load from one of the tandem axles tothe other, thereby to secure-a distribution of the load between the tandem axles. At the same-time the torsion rod 90 is of sufficient length to provide the necessary resiliency between. the tandem axles 30-, 31 and the frame 20 of the truck.

It will be seen that the shackles $8 and 68a are inclined. upwardly and inwardly from their respective crank arm pivots 'Il', Ila to the correspondin axle pivot. pins 43, 43a; This upward and. inward. inclined arrangement of the shackles tends to cause each axle to centralize itself in a direction transverse of the frame and enables the action of gravity to geometrically and resiliently resist any movement of either axle away from its central position. This permits the vehicle frame 20 to move substantially straight ahead despite a certian amountof lateral movement of the axles. This arrangement of the. shackles further provides" high and wide pivot positions which provide increasedstab-ility in. thatthese high and-wide pivot positions. provide effective spring centers which can be as wideorzwider than the track of the vehicle. Further, this arrangement reduces side sway, the high and. Wide pivot positions, together with the upward and mward slant. of the shackles, providing a suspension in which the frame 20 is more nearly suspended than mounted Other important advantages which flow from: the inclined arrangement of the shackles as shown are the reduction in. the possibility: of wheel tramp and inthe elimination of. the need for antibody-rolldevices, such as torsion bar stabilizers. I 1

When the vehicle is traveling' straight ahead, if the tandem axles .30, 3| are not parallel for any reason, they will automatically assume a parvalleliposition because: of the fact that if, for example, the rearfiaxle (H is outof" line, itwill tend to fol low a horizontal arc and this tendency, due to the lateral friction between the tires and the roadway, will cause'a lateral movement of the axle relative to the frame. Due to the fact that the shackles 68s and 68a normally extend upwardly and inwardly, this lateral movement is automatically caused to be translated into a slight turning movement, in a horizontal plane, of the whole axle, and this turning; movement will con tinue until both the tandem axlesv are in line with. each other. Such a movement, naturally, a uses. a change in the angul'arity of the shackles E8 or 6811 at the opposite end of each axle and this: change is resi'stedaby gravity which, due to the obliquity of theshackles, is" caused toact in a geometric manners This tendency of. theaxles 30' and (H to trail each other also occurs when the axle is making aturn on the road'. In this case, just-as when going straight ahead, the tires naturally tend to resist. lateral: scuffing and in doing so tend to push each axlelaterally, and, as-a consequence; each axle: moves axially to eliminate this scufii ng.

confining our attention to, say, the fronttand'em axle 30, this lateral or axial movement of the axle resisting'tire scuff' on making a turn causes shackles 68, crank arms 'M'and vehicle frame 2 0,

it will be seen that-such rotation or oscillation of the shackles 58*rel'ative tothe axle pivot pins 43 will cause endwise displacement of the axle pivot pins E3. Since the axle" pivot pins 43 are held against endwi'se'displacement relative to the axle 30', it will be seen that such endwise displacement of the axle pivot pins 43" will cause a foreand -aft displacement of the corresponding end of the axle f30' relative to" the frame 20". The grooves 44 in theaxle pivot pin 43 at one end of the axle 3'0 spiral in theopposite direction from: the grooves 44' in the axle pivot pin 43" at the opposite end of the axle. Accordingly, on rounding acurve and with suchendwise movement of the axle 30 causing its shackles 68 to swing relative to its axlepivot pins 43, one end of the axle 30 is moved rearwardly, relativeto the .vehicle frame 20, by the spiral groove 44 in the adjacent axle pivot pin 43 while the opposite end of the axle 30 is moved forwardly, relative to the -vehicle frame 20, by the spiral groove 44 in the other axle pivot pin 43. The spiral grooves 44 are, of course, arranged to spiral in that direction to cause the axle 30 to steer in the direction to correspond to the turn being made by the truck. That is, these grooves 44 spiral in the direction, as shown, such that when making, say, a left hand turn, the spiral groove 44 in the left hand axle pivot pin 43 will cause a rearward .movement, relative to the vehicle frame 20, of the'left hand end of the axle 30 whereas the spiral grooves 44 in the right hand axle pivot pin 43 will cause a forward movement, relative to the :vehicle frame 20, of the right hand end of the axle 30.

This description of the self-steering action of the front tandem axle 30 caused by its helically grooved or threaded axle pivot pins 43 applies also to the rear axle 3! which is similarly provided with a pair of helically grooved axle pivot pins 43a. With both the front and rear axles the pitch of the helical groove on the axle pivot pins is such as to cause at least inch movement of each axle end lengthwise of the truck frame in response to a 60-70 movement of the corresponding shackle. With such helically grooved axle pivot pins, when the truck is making a turn, the tandem axles can be caused to automatically move to such oblique position relative to each other as will cause their axes to intersect the axes of rotation of the two front or steering wheels of the truck and thereby enable the truck to make the turn without tire scuffing. This action occurs when either the vehicle is steered around a long turn in the road or when it, is steered sharply on a straight road, a for instance, when overtaking a slow vehicle ahead, or otherwise avoiding some obstruction. It will also be seen that this action takes place to some extent when a tendency to tire scufling occurs because one wheel or a pair of wheel having .a diameter different from the diameter of the wheel or pair of wheels at the other end of the same axle.

In achieving such self-steering of the tandem axles, it is only necessary to thread or helically groove the four axle pivot pins 43 and 43a. The other pins, namely the crank arm pivot pins and the pins supporting the crank arms can be of conventional form, threaded bushing being preferred for these pins merely in the interest of economy, the action of the threads having no effect in steering the axles.

It will be noted that with the suspension as shown, the torsion rods 90 and tubes 16 are disposed within the frame 20 and in particular are not arranged between the frame and the axles. This renders it unnecessary to raise the frame to accommodate the suspension and hence permits the truck to be made with a lower frame than was possible with the construction shown in my Patent No. 2,333,650. This is an important feature of the invention since low a Well as wide truck bodies are in increasing demand.

It will be further noted that while the openings I5 inthe longitudinal side frame bars 21 are provided at a point where the frame is highly stressed in order to accommodate the forward crank arms 14, these openings are relatively small and are in the web of these longitudinal side frame bars and leave the upper and lower flange thereof intact. Further, at this point the longitudinal side frame bars 2| can be'readily reinforced as by the top plates 26 shown. The recess H2 for the gear box I04 is larger than the opening 15 and also cuts throughthe lower flange of each longitudinal side frame bar 2|. However, these recesses H2 are at the extreme rear of the frame where the frame is not highly stressed.

From the foregoing it will be seen that the invention is particularly applicable to trucks having low and wide frames and large tires and achieves the stated objects in a simple and inexpensive construction.

I claim:

1. A tandem axle vehicle spring suspension adapted to be interposed between a vehicle frame having a longitudinalside bar at one side and a pair of tandem axles each having wheels journalled thereon, comprising a pair of coaxial bearings secured directly to the inner side of said longitudinal side bar on opposite sides of the front tandem axle, a tube journalled in said bearings to extend lengthwise of said longitudinal side bar along the inner side and above the lower edge thereof, mean operatively connecting said tube intermediate said bearings with the corresponding end of said front tandem axle, a torsion rod in said tube, means securing the front end of said torsion rod to the front end of said tube, said torsion rod extending rearwardly to a position beyond the rear tandem axle, a gear box secured to said longitudinal side bar in rear of said rear tandem axle, a pair of intermeshing gears journalled in said gear box one above the other to rotate about parallel axes and with the upper gear arranged generally coaxial with said pair of bearings, means securing the rear end of said torsion rod to said upper gear, and means operatively connecting said lower gear with the corresponding end of said rear tandem axle.

2. A tandem axle vehicle spring'suspension adapted to be interposed between a vehicle frame having a longitudinal side bar at one side and a pair of tandem axles each having wheels journalled thereon, comprising a bearing secured to the inner side of said longitudinal side bar adjacent the front tandem axle, a torsion rod having its front end journalled in said bearing and arranged parallel with and above the lower edge of said longitudinal side bar, means operatively connecting the front end of said torsion rod with the corresponding end of said front tandem axle, said torsion rod extending rearwardly to a position beyond the rear tandem axle, a gear box secured to said longitudinal sidebar in rear of said rear tandem axle, a pair of intermeshin gear journalled in said gear box one above the other to rotate about parallel axes and with the upper gear arranged generally coaxially with said bearing, means securing the rear end of said torsion rod to said upper gear, and means operatively connecting said lower gear with the corresponding end of. said rear tandem axle.

3. A tandem axle vehicle spring suspension adapted to be interposed between a vehicle frame having a longitudinal side bar at one side and a pair of tandem axles each having wheels journalled thereon, comprising a pair of bearings secured to said longitudinal side bar and disposed coaxially along the inner side thereof, a crank arm journalled in said bearings and extending horizontally through an opening provided in said longitudinal sidebar intermediate said bearings,

a shackle connecting the freeend' of said crank arm with the corresponding, end of the front tandem axle, a torsion rod secured to said crank arm to extend rearwardly therefrom generally coaxially with its fulcrum axis and arranged above the lower edge of said longitudinal side bar; andv means operatively connecting. the rear end of. saidtorsion rodv with. the corresponding end of the rear tandem axlezz. t a

4. A tandem axle vehicle spring suspension adapted to be interposed between a vehicle frame having a longitudinal side bar at one side and a pair of tandem axles each having wheels journalled thereon, comprising a pair of bearing secured to said longitudinal side bar and disposed coaxially along the inner side thereof, a tube iournalled in said bearings to extend lengthwise of said longitudinal side bar along the inner side and above the lower edge thereof, a crank arm fast to said tube intermediate said bearings and extending horizontally through an opening provided in said longitudinal side bar, a shackle connecting the free end of said crank arm with the corresponding end of the front tandem axle, a torsion rod secured to said crank arm to extend rearwardly therefrom generally coaxially with its fulcrum axis and arranged above the lower edge of said longitudinal side bar, and means operatively connecting the rear end of said torsion rod with the corresponding end of the rear tandem axle.

5. A tandem axle vehicle sprin suspension adapted to be interposed between a vehicle frame having a longitudinal side bar at one side and a pair of tandem axles each having wheels journalled thereon, comprising a pair of bearings secured to said longitudinal side bar and disposed coaxially along the inner side thereof, a crank arm journalled in said bearings and extending horizontally through an opening provided in said longitudinal side bar intermediate said bearings, a shackle connecting the free end of said crank arm with the corresponding end of the front tandem axle, a torsion rod secured to said crank arm to extend rearwardly therefrom generally coaxially with its fulcrum axis and arranged above the lower edge of said longitudinal side bar, a gear box secured to said longitudinal side bar in rear of said rear tandem axle and projecting into a recess provided in said longitudinal side bar, a pair of intermeshing gears journalled in said gear box one above the other to rotate about parallel axes and with the upper gear arranged generally coaxial with said pair of bearings, means securin the rear end of said torsion rod to said upper gear, and means operatively connecting said lower gear with the corresponding end of said rear tandem axle.

6. A tandem axle vehicle spring suspension adapted to be interposed between a vehicle frame having a longitudinal side bar at one side and a pair of tandem axles each having wheels journalled thereon, comprising a pair of bearings secured to said longitudinal side bar and disposed coaxially along the inner side thereof, a crank arm journalled in said bearings and extending horizontally through an opening provided in said longitudinal side bar intermediate said bearings, a shackle connecting the free end of said crank arm with the corresponding end of the front tandem axle, a torsion rod secured to said crank arm to extend rearwardly therefrom generally coaxially with its fulcrum axis and arranged above the lower edge of said longitudinal side bar, a gear box secured to said longitudinal side 'jectingint'o a recessprovided in said longitudinal side. bar a-pair of intermeshing gears journalled in said :gear box-one above the other to rotate about parallel axessand with the upper gear arranged generally coaxial with said pair' of-bearings, means securing :the rear end of said torsion rod to said upper gear,aa. second crank arm arranged generally horizontally above: said rear tandem axle, a bearing on said longitudinal side barin'fr'ont ofsaidrear tandem axle generally coaxial with said lower gear and in which the forward end of said second crank arm is fulcrumed, means securing the rear end of the fulcrum of said second crank arm to said lower gear, and a shackle connecting the free end of said second crank arm with the corresponding end of said rear tandem axle.

7. A tandem axle vehicle spring suspension adapted 'to be interposed between a vehicle frame having a longitudinal side bar at one side and a pair of tandem axles each having wheels journaled thereon, comprising a crank arm fulcrumed on said longitudinal side bar above the front tandem axle to swing about a generally horizontal axis parallel with said longitudinal side bar, said crank arm projecting outwardly from said longitudinal side bar, a shackle pivotally connecting the outer free end of said crank arm with the corresponding end of said front tandem axle, a gear box secured to said longitudinal side bar in rear of the rear tandem axle, a pair of intermeshing gears journalled in said gear box one above the other to rotate about parallel axes and with the upper gear arranged generally coaxial with the fulcrum axis of said crank arm, a torsion rod connected at its front end with the fulcrum of said crank arm and at its rear end with said upper gear, a second crank arm arranged generally horizontally above said rear tandem axle, a bearing on said longitudinal side bar in front of said rear tandem axle generally coaxial with said lower gear and in which the forward end of said second crank arm is fulcrumed, means securing the rear end of the fulcrum of said second crank shaft to said lower gear, and a shackle connecting the free end of said second crank arm with the corresponding end of said rear tandem axle.

8. A tandem axle vehicle spring suspension adapted to be interposed between a vehicle frame having a longitudinal side bar at one side and a pair of tandem axles each having wheels journalled thereon, comprising a crank arm fulcrumed on said longitudinal side bar above the front tandem axle to swing about a generally horizontal axis parallel with said longitudinal side bar, said crank arm projecting outwardly from said longitudinal side bar, a shackle pivotally connecting the outer free end of said crank arm with the corresponding end of said front tandem axle, a gear box secured to said longitudinal side bar in rear of the rear tandem axle, a pair of intermeshing gears journalled in said gear box one above the other to rotate about parallel axes and with the upper gear arranged generally coaxial with the fulcrum axis of said crank arm, a torsion rod connected at its front end with the fulcrum of said crank arm and at its rear end with said upper gear, a second crank arm arranged generally horizontally above said rear tandem axle, a bearing on said longitudinal side bar in front of said rear tandem axle generally coaxial with said lower gear and in which the forward end of said second crank arm is fulcrumed, the rear end of said second crank arm being formed to provide a fulcrum hub rojecting into the front end of a crank arm and having its rear end splined to said lower gear, and a shackle connecting the free end of said second crank arm with the corresponding end of said rear tandem axle.

ALBERT F. HICKMAN.

18 REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date Beatty Nov. 8, 1921 Mercier Nov. 23, 1937 Holmstrom et a1. Sept. 30, 1947 

